As an FPS player that uses crouch a lot, I'm not a fan of the mechanical keyboards. The extra needed power to push and hold down on the buttons compared to a membrane keyboard can get tiresome for my pinky over long sessions.

You need to start playing Ghost Recon and ARMA, those let you switch between three stances.(actually, the two GRAW games give you four options, but not the orig GR)

I do not know about others but I use my thumb for crouch.. I am still interested in getting one of these keyboards.